In some types of electric motors, controlling the motor is based in part on its rotor position. For example, permanent magnet (PM) synchronous motors utilize rotor position information for accurate torque control. The rotor position is typically measured with a resolver or a similar rotation sensing device. The rotor of the resolver is coupled to the machine rotor of the PM synchronous motor. For vector control, the resolver is generally aligned to the north pole of the machine rotor magnet (e.g., aligned with a controller d-axis). The accuracy by which the resolver can be aligned typically influences the accuracy and performance of the motor control.
In some electric motors, the resolver is aligned during the assembly process. A high degree of precision is typically desired from the alignment process, which is generally provided by individually testing each electric motor and manually adjusting the resolver. For large volume manufacturing, this alignment process may be costly, time consuming, and complicated. One sensorless motor control technique injects a high frequency voltage signal (e.g., in the range of about 500 Hz to about 2 kHz) into the stator of the electric motor and measures the current produced in response to the high frequency signal. The measured current is used to estimate the resolver alignment. Acoustic noise is generated when the high frequency signal has a large magnitude. Additionally, the frequency range commonly associated with the high frequency signal is within a sensitive range for humans. Further, the high frequency signal method is poorly suited for machines with inherently low saliency, such as surface mount PM motors.
Accordingly, it is desirable to provide a method and system for resolver alignment in electric motor systems that minimize assembly and manufacturing costs associated with the electric motor systems. Additionally, it is desirable to provide a method and system for resolver alignment that minimize acoustic noise generation. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.